# Lesson Tutor : Algebra : Grade 9 : Introducing positive and negative numbers

Algebra Lesson 9 – Positives and Negatives on the Number Line
by Elaine Ernst Schneider

Objective(s): By the end of this lesson the student will be able to:

Pre-Class Assignment: Review/ completion of Algebra Lesson 8

Resources/Equipment/Time Required:

Outline:

Different kinds of numbers are used to stand for different things. There are positive numbers and there are negative numbers. Positive numbers are more than zero and negative numbers are less than zero.

The best way to “see” negative and positive numbers is to look at a number line:

/_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/_____/

-7 … -6 ….. -5 …. -4 …… -3 …… -2 ….. -1 ….. 0 …… 1 …… 2 …… 3 …… 4 …… 5 …… 6 …… 7

When you use a number line, you add positives as you go to the right and you add negatives as you move to the left. For example, 3 + -2 means that you start at 3 and move two places to the left. The answer is 1. To add a positive to a negative, you work from left to right. For example, -4 + 3 is -1. You get that by starting at -4 and moving three places to the right. To add two negatives, move to the left. For example, -1 + -3 = -4. You arrive at that answer by starting at -1 and counting three places to the left.

Now you try:

1.    1 + -1
2.    4 + -2
3.    2 + 4
4.   -2 + -5
5.   -5 + 4
6.   – 3 + 5
7.   -2 + -2 + -1
8.   -5 + 6
9.   -7 +2
10   -4 + -2 + 2
Now try a few that are beyond the scope of the number line shown above. You can do it! Just use the principles you have learned.

1. -15 + 13
2. -39 + -40
3. -23 + 20
4. 2 + -11
5. -13 + -4

CUT HERE_________________________________________________________________

1.    0
2.    2
3.    6
4.    -7
5.    -1
6.     2
7.    -5
8.     1
9.    -5
10   -4
********

1. -2
2. -79
3. -3
4. -9

-17

Pre-Requisite To:  Algebra Lesson 10